Effects of the Photooxidant on DNA-Mediated Charge Transport

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• 作者：Tashica T. Williams ; Chikara Dohno ; Eric D. A. Stemp ; and Jacqueline K. Barton
• 刊名：Journal of the American Chemical Society
• 出版年：2004
• 出版时间：July 7, 2004
• 年：2004
• 卷：126
• 期：26
• 页码：8148 - 8158
• 全文大小：238K
• 年卷期：v.126,no.26(July 7, 2004)
• ISSN：1520-5126

文摘

A direct comparison of DNA charge transport (CT) with different photooxidants has been made.Photooxidants tested include the two metallointercalators, Rh(phi)₂(bpy')³⁺ and Ru(phen)(bpy')(dppz)²⁺,and three organic intercalators, ethidium (Et), thionine (Th), and anthraquinone (AQ). CT has been examinedthrough a DNA duplex containing an A₆-tract intervening between two 5'-CGGC-3' sites with each of thephotooxidants covalently tethered to one end of the DNA duplex. CT is assayed both through determinationof the yield of oxidative guanine damage and, in derivative DNA assemblies, by analysis of the yield of afaster oxidative trapping reaction, ring opening of N²-cyclopropylguanine (d^CPG) within the DNA duplex.We find clear differences in oxidative damage ratios at the distal versus proximal 5'-CGGC-3' sites dependingupon the photooxidant employed. Importantly, nondenaturing gel electrophoresis data demonstrate theabsence of any DNA aggregation by the DNA-bound intercalators. Hence, differences seen with assembliescontaining various photooxidants cannot be attributed to differential aggregation. Comparisons in assembliesusing different photooxidants thus reveal characteristics of the photooxidant as well as characteristics ofthe DNA assembly. In the series examined, the lowest distal/proximal DNA damage ratios are obtainedwith Ru and AQ, while, for both Rh and Et, high distal/proximal damage ratios are found. The oxidativedamage yields vary in the order Ru > AQ > Rh > Et, and photooxidants that produce higher distal/proximaldamage ratios have lower yields. While no oxidative DNA damage is detected using thionine as aphotooxidant, oxidation is evident using the faster cyclopropylguanosine trap; here, a complex distancedependence is found. Differences observed among photooxidants as well as the complex distancedependence are attributed to differences in rates of back electron transfer (BET). Such differences areimportant to consider in developing mechanistic models for DNA CT.